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Standard

Energy barrier

ActivePublished: 28 October 2026Updated: 28 October 2026Published
Key innovation
Caps the electrical energy (voltage and current) entering the hazardous area below the ignition threshold of the explosive atmosphere, instead of mechanically containing the spark source.
Category
Standard
Abstraction level
Standard
Operation level
DeploymentRobot control
Use cases
Powering sensors and transmitters in Ex zonesIntrinsically safe 4-20 mA signal loopsInstrumentation and communication in refineries and chemical plantsRobotics and automation in explosive atmospheresProtecting control circuits in mining and gas industries

How it works

The barrier is installed in the safe area, on the line connecting the power supply/controller to the device in the hazardous area. In a Zener barrier, current is limited by a series fail-open resistor, voltage is clamped by redundant Zener diodes, and a fuse disconnects the circuit when the diodes conduct; excess potential is diverted to an intrinsically safe earth. In a galvanically isolated barrier, the safe- and hazardous-side circuits are separated by a layer of insulation (transformers/optocouplers) and energy is limited on the output side with no shared ground. Barrier selection follows the entity concept: the barrier output parameters (Uo, Io, Po) must not exceed the permitted apparatus input parameters (Ui, Ii, Pi), while the permitted external capacitance and inductance (Co, Lo) must exceed the combined capacitance/inductance of the apparatus and cable (Ci, Li).

Problem solved

Electrical and instrumentation equipment operating in explosive atmospheres can produce a spark or reach the ignition temperature of the surrounding atmosphere. The problem is how to power such circuits and exchange signals with them without delivering enough energy into the zone to cause ignition.

Components

Current-limiting resistorLimits the maximum output current (Io)

A series fail-open resistor that fails to an open circuit.

Zener diodes (voltage clamp)Limit the maximum output voltage (Uo)

Redundant Zener diodes clamp the voltage to a safe level regardless of the input supply.

FuseDisconnects the circuit when the diodes conduct fault current

A current-limiting fuse protecting the Zener diodes from overload.

Galvanic isolation stageIsolates the safe side from the hazardous side (in isolated barriers)

Transformers or optocouplers separating the circuits, removing the need for a shared intrinsically safe earth.

Implementation

Implementation pitfalls
Entity parameter mismatchCritical

Barrier output parameters (Uo, Io, Po) exceeding the permitted apparatus input parameters (Ui, Ii, Pi), or too small a permitted external capacitance/inductance (Co, Lo) relative to the Ci, Li of the apparatus and cable, void the intrinsic safety of the whole loop.

Fix:Verify the entity-parameter match of barrier, apparatus and cable before commissioning the loop.
Improper intrinsically safe earthHigh

A Zener barrier requires a reliable, low-impedance intrinsically safe earth; a missing or faulty earth prevents excess energy from being diverted.

Fix:Use a dedicated, certified IS earth, or choose a galvanically isolated barrier.

Evolution

2014
ATEX Directive 2014/34/EU

EU legal framework for equipment and protective systems for explosive atmospheres, covering intrinsically safe barriers.

ATEX (concept)
2015
Introduction of IEC TS 60079-39

Technical specification for intrinsically safe systems with electronic spark/energy limitation.

2023
IEC 60079-11:2023 โ€” current edition of the standard
Inflection point

The current edition of 'Explosive atmospheres โ€” Part 11: Equipment protection by intrinsic safety "i"'.